In cellular networks, allocation of radio resources to a certain user equipment (UE), also referred to as scheduling, is typically accomplished dynamically on the network side. In the downlink (DL) direction from the cellular network to the UE, a network node may allocate radio resources in accordance with a need to transmit DL data to the UE. The network node may then inform the UE about the allocated resources by sending a DL assignment. For the uplink (UL) direction from the UE to the cellular network, a scheduling request which is sent by the UE to the cellular network may be used to indicate that the UE needs radio resources for sending UL data. For example, in the LTE (Long Term Evolution) radio access technology specified by 3GPP (3rd Generation Partnership Project), a base station of the LTE radio access technology, referred to as “evolved Node B” (eNB) is responsible for the scheduling. This may be accomplished dynamically, taking into account the instantaneous traffic pattern and radio propagation characteristics of each UE.
In the dynamic scheduling process of the LTE radio access technology a UE which needs to send UL data may first send a scheduling request to an eNB which serves the cell of the UE. The scheduling request may be sent on a UL control channel, referred to as PUCCH (Physical UL Control Channel), providing dedicated resources for sending scheduling requests by the UE. Alternatively, the scheduling request may be sent on a contention based random access channel (RACH). The eNB then allocates UL radio resources to the UE. The allocated UL radio resources are indicated in a UL grant, which is sent from the eNB to the UE. A separate UL grant is sent for each subframe or TTI (Transmission Time Interval) of 1 ms. On the allocated UL radio resources, the UE may then send UL data to the eNB. In addition, the UE may also send a buffer status report (BSR) indicating the amount of buffered UL data still to be sent by the UE.
In the above process of transmitting the UL data, latency occurs which is due to the sending of the scheduling request before the UE can proceed with the transmission of the UL data. However, such delay is not desirable in many cases. For example, certain data traffic may be sensitive to latency, such as data traffic associated with online gaming.
A technology which may be used for achieving a reduced latency is Semi-Persistent Scheduling (SPS) as specified in 3GPP TS 36.321 V12.2.1 (2014-06). In SPS, UL radio resources are periodically allocated to the UE by sending a long lasting grant that which covers multiple TTIs by allocating UL radio resources in a pattern of TTIs with configurable periodicity. By utilizing SPS, the need to send of scheduling requests may be reduced.
However, to achieve a certain latency by utilizing SPS, it may be necessary to configure the allocated SPS UL radio resources with a short periodicity. This may result in allocating more UL radio resources to the UE than actually required. Nonetheless, the UE needs to perform a UL transmission on ail allocated UL radio resources, which means that UL transmissions are filled by padding. This sending of padding UL transmissions may cause undesired energy consumption on the UE side and may also increase interference.
Accordingly, there is a need for techniques which allow for efficiently controlling radio transmissions in a cellular network, in particular with respect to UL transmissions with low latency.